Write and solve an equation of ratios here. Let x be the amount of butter needed if 3 cups of flour are used. Then, comparing the quantities of butter first (in the first column) and the quantities of flour second, we get the ratio
x 3 cups
------------- = -------------
(4/5) cup 2 cups
Cross-multiplying, we get:
2x = 12/5, or x = 6/5
You'll need 6/5 cups of butter, or 1 1/5 cups, if you're using 3 cups of flour.
so the circle has a radius of 4, and the square has all sides of 8, we can simply get the area of the square, and the area of the circle, and subtract the area of the circle, what's leftover, is just the shaded area.